Beer measurement

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A hydrometer floating in a test jar of wort. The specific gravity reading is approximately 1.050.

When drinking beer, there are many factors to consider. Principal among them are bitterness, the variety of flavours present in the beverage, along with their intensity, alcohol content, and colour. Standards for those characteristics allow a more uniform determination to be made on the overall quality of any beer.

Colour[edit]

"Degrees Lovibond" or "°L" scale is a measure of the colour of a substance, usually beer, whiskey, or sugar solutions. The determination of the degrees lovibond takes place by comparing the colour of the substance to a series of amber to brown glass slides, usually by a colorimeter. The scale was devised by Joseph Williams Lovibond.[1] The Standard Reference Method (SRM) and European Brewery Convention (EBC) methods have largely replaced it, with the SRM giving results approximately equal to the °L.

The Standard Reference Method or SRM[2] is a system modern brewers use to measure colour intensity, roughly darkness (but see Tristimulus Colour below), of a beer or wort. The method involves the use of a spectrophotometer or photometer to measure the attenuation of light of a particular wavelength, 430 nanometres, as it passes through a sample contained in a cuvette located in the light path of the instrument.

The EBC convention also measures beer and wort colour, as well as quantifying turbidity (also known as haze) in beer.

Colour based on Standard Reference Method (SRM)
SRM/Lovibond Example Beer color EBC
2 Pale lager, Witbier, Pilsener, Berliner Weisse 4
3 Maibock, Blonde Ale 6
4 Weissbier 8
6 American Pale Ale, India Pale Ale 12
8 Weissbier, Saison 16
10 English Bitter, ESB 20
13 Biere de Garde, Double IPA 26
17 Dark lager, Vienna lager, Marzen, Amber Ale 33
20 Brown Ale, Bock, Dunkel, Dunkelweizen 39
24 Irish Dry Stout, Doppelbock, Porter 47
29 Stout 57
35 Foreign Stout, Baltic Porter 69
40+ Imperial Stout 79

Strength[edit]

The "Plato scale" is an empirically derived hydrometer scale to measure density of beer wort in terms of the extract's percentage by mass. It was developed in 1843 by Bohemian scientist Karl Balling as well as Simon Ack, and improved by German Fritz Plato. The scale expresses the density as the percentage of sucrose by mass, so a wort measured at 12° Plato has the same density as a water – sucrose solution containing 12% sucrose by mass, denoted as 12% Brix. For the brewer, it has an advantage over specific gravity in that it expresses the measurement in terms of the amount of fermentable materials; of course, as wort or must is composed of more solids than just sucrose, it is not exact. Degrees Plato are more popular in central European brewing, and occasionally feature in beer names.

The relationship between degrees Plato and specific gravity (SG) is not linear, but a good approximation is that 1° Plato equals four “brewer’s points” (4 x .001); thus 12° Plato corresponds to an SG of 1.048 [1+(12 x 4 x .001)]. Gravity refers to the specific gravity of the wort or must at various stages in the fermentation. This article focuses primarily on the brewing industry. The concepts and equations are basically the same in the wine making industry.

At various stages in alcohol fermentation, the density of the wort varies. Depending upon the depth that the hydrometer falls into the wort, the percentage of alcohol can be determined. Initially (before alcohol production by the yeast commences) the specific gravity of a wort is dependent mostly on the amount of sugar present and, therefore, specific gravity readings can be used to determine sugar content by the use of formulae or tables. This sugar content is expressed in units of grams of sugar per 100 grams of wort (that is, it is expressed as a percentage by mass) and called, in the brewing industry, "degrees Plato" (abbreviated °P) and in the wine industry "degrees Brix"; there is a difference between these units, but it is so insignificant that they may be used virtually interchangeably. Even when specified in terms of °P, it is correct and not uncommon to refer to the pre-fermentation reading as the "Original Gravity" (abbreviated OG), though it is more correctly termed the "Original Extract" (abbreviated OE). By considering the original sugar content, the brewer or vintner obtains an indication as to the probable ultimate alcoholic content of his product. The OE is often referred to as the "size" of the beer and is, in Germany, often printed on the label as Stammwürze or sometimes just as a percent. In the Czech Republic, for example, people speak of "10 degree beers", "12 degree beers" and so on.

As fermentation progresses, the yeast convert sugars to carbon dioxide, ethanol, more yeast, and flavour-producing compounds. The decline in the sugar content and the presence of ethanol (which is appreciably less dense than water) both contribute to a lowering in the specific gravity of the wort, so that the formulae relating sugar content and specific gravity no longer apply. Nevertheless, by monitoring the decline in SG over time, the brewer obtains information about the health and progress of the fermentation and determines that it is complete when gravity stops declining. A gravity measurement taken at this time compared to the original gravity reading can be used to estimate the amount of sugar consumed and thus the amount of ethanol produced. Specific gravity is measured by a hydrometer, pycnometer, or oscillating U-tube electronic meter.

Gravity measurements are used to determine the "size" of the beer, its alcoholic strength, and how much of the available sugar the yeast were able to consume (a given strain can be expected, under proper conditions, to ferment a wort of a particular composition to within a range of attenuation; that is, they should be able to consume a known percentage of the extract).

Alcohol by volume (abbreviated as abv or ABV) is a standard measure of how much alcohol (ethanol) is contained in an alcoholic beverage (expressed as a percentage of total volume).[3][4][5] The abv standard is used worldwide.[6]

In some countries,[which?] alcohol by volume is referred to as degrees Gay-Lussac (after the French chemist Joseph Louis Gay-Lussac).[7]

XXX marks[edit]

See also: Food grading

The letter "X" is used on some beers, and was traditionally a mark of beer strength, with the more Xs the greater the strength. Some sources suggest that the origin of the mark was in the breweries of medieval monasteries.[8] Another plausible explanation is contained in a treatise entitled "The Art of Brewing" published in London in 1829. It says; "The duties on ale and beer, which were first imposed in 1643... at a certain period, in distinguishing between small beer and strong, all ale or beer, sold at or above ten shillings per barrel, was reckoned to be strong and was, therefore, subjected to a higher duty. The cask which contained this strong beer was then first marked with an X signifying ten; and hence the present denominations of XX (double X) and XXX (triple X) on the casks and accounts of the strong-ale brewers".[9]

In mid-19th century England, the use of "X" and other letters had evolved into a standardised grading system for the strength of beer.[10] Today, it is used as a trade mark by a number of brewers in the United Kingdom, the Commonwealth and the United States.

Bitterness[edit]

See also: Hops § Brewing

Bitterness scales attempt to rate the perceived relative bitterness of beer. The bitterness of beer is provided by compounds such as isohumulones from hops used during brewing.

The International Bittering Units scale, or simply IBU scale, is measured through the use of a spectrophotometer and solvent extraction[11] a calculation is performed on this absorbance to give a result in IBU.[12] This technique was adopted at the same time as another method based on measuring the concentration (in milligrams per litre; parts per million w/v) of IAA isomerized α acids in a beer, causing some confusion among small-scale brewers.[13] The American Society of Brewing Chemists, in the introduction to its methods on measuring bitterness, points out some differences between the results of the two methods:

While the results of the IAA methods are practically identical to those obtained by the [I]BU method for beer brewed with fresh hops, the IAAs of beer brewed with old or poorly stored hops, and with certain special hop extracts, can be significantly lower than the [I]BU figure.[11]

The European Bitterness Units scale, often abbreviated as EBU, is a bitterness scale[14] in which lower values are generally "less bitter" and higher values "more bitter". The scale and method are defined by the European Brewery Convention, and the numerical value should be the same as of the International Bitterness Units scale (IBU), defined in co-operation with the American Society of Brewing Chemists.[15] However, the exact process of determining EBU and IBU values differs slightly, which may in theory result with slightly smaller values for EBU than IBU.[16]

IBU can not be determined by perceived bitterness. For example, the bittering effect of hops is less noticeable in beers with a high quantity of malt, so a higher bitterness is needed in heavier beers to balance the flavour and achieve the same perceived bitterness as compared to a lighter beer. For example, an Imperial Stout may have an IBU of 50, but will taste less bitter than an English Bitter with an IBU of 30, because the latter beer uses much less malt than the former. After around 100 IBU, hop utilization is so poor that the number ceases to be meaningful in regards to taste, although continued hop additions will increase bitterness. Many IPAs are well above 100 theoretical IBU.[citation needed] Light lagers without much bitterness will generally have 8-20 IBU, while an India Pale Ale may have 60-100 IBU or more.[17]

Automated combined systems[edit]

For high-through-put applications (as in quality control labs of big breweries for example), automated systems are available. Simple systems work with adjustment data blocks for each kind of beer, high-end systems are matrix-independent and give correct results for e.g. alcohol strength, extract content, pH, colour, turbidity, CO2 and O2 without any product-specific calibration.

Latest innovations are packaged beverage analyzers, that measure directly out of the package (glass bottle, PET bottle or can) and give several parameters in one measuring cycle without any sample preparation (no degassing, no filtering, no temperature conditioning).[18]

Oxidative degradation measurement[edit]

Oxidative deterioration of beer can be measured by the way of chemiluminescence[19] or by electron spin resonance.[20] Automated systems exist to determine the lag time of beer related to the antioxidant capacity to resist oxidative spoilage of flavours.[21]

Software[edit]

Software tools are available to brewers to formulate and adapt recipes with a view to accurately measure the various values in brewing. Data can be exchanged in formats such as BeerXML to allow for accurate replication of recipes at remote sites or the adaptation of recipes to account for variations in locally available water, mash ingredients, hops etc.

See also[edit]

Notes and references[edit]

  1. ^ Article at BrewWiki.com
  2. ^ "Beer 10-A Spectrophotometric Color Method", ASBC Methods of Analysis
  3. ^ "Lafayette Brewing Co. Beer Terms". www.lafayettebrewingco.com. Archived from the original on 25 July 2008. Retrieved 2008-07-05. 
  4. ^ "Glossary of whisky and distillation". www.celtic-whisky.com. Archived from the original on 5 July 2008. Retrieved 2008-07-05. 
  5. ^ "English Ales Brewery Monterey British Brewing Glossary". www.englishalesbrewery.com. Archived from the original on 4 July 2008. Retrieved 2008-07-05. 
  6. ^ "Frequently Asked Questions - CAMRA". www.camra.org.uk. Retrieved 2008-07-05. 
  7. ^ "Joseph Louis Gay-Lussac (1778 – 1850)". chemistry.about.com. Retrieved 2008-07-05. 
  8. ^ Bamforth 2008, p. 34-.
  9. ^ Booth 1829, p. 2–.
  10. ^ http://www.europeanbeerguide.net/beer_strengths_1860_1900.pdf
  11. ^ a b "Methods of Analysis". American Society of Brewing Chemists. 1996. pp. Beer – 23:1–4.  |chapter= ignored (help)
  12. ^ Rabin & Forget 1998, p. 43.
  13. ^ "What Is an IBU…Really?". Basic Brewing Radio. Season 4. Episode 12. 2008–03–20.
  14. ^ Lehigh Valley Homebrewers (2007). "Beer and Brewing Glossary". Retrieved 2009-08-05. IBUs (International Bittering Units) - The accepted worldwide standard for measuring bitterness in beer, also known as EBU, based on the estimated alpha acid percentage of the hops used and the length of time they are boiled. 
  15. ^ European Brewery Convention. "The Analysis Committee". Retrieved 2009-08-05. The EBC Analysis Committee also works closely together with the 'American Society of Brewing Chemists' (ASBC) to establish so-called 'International methods' with world-wide recognition of applicability. A partnership declaration between EBC and ASBC has been signed. The integration of the IOB methods of analysis and EBC methods is nearing completion. 
  16. ^ ajdelange (2009-06-11). "Difference between IBU and EBU". Retrieved 2009-08-05. Because the absorption decreases pretty quickly with time at the completion of extraction the EBC reported value will, in general, be a little smaller than ASBC reported value unless the beer requires centrifugation. For all practical considerations the two systems should give the same results. 
  17. ^ Crouch 2006, p. 263–.
  18. ^ "Anton Paar". www.anton-paar.com. 
  19. ^ Kaneda et al. 1990.
  20. ^ Kaneda et al. 1988.
  21. ^ e-scan-beer-method

External links[edit]